A currently available tracked agricultural tractor includes a walking beam suspension which supports the front of the chassis on left and right track assemblies. U.S. Pat. No. 4,209,072 shows a wheeled agricultural tractor which includes a walking beam suspension which supports the front of the chassis on left and right wheel assemblies. These walking beams are connected to the chassis by a fixed pivot pin. This permits the track or wheel assemblies to pivot or oscillate with respect to the chassis about a fore-and-aft axis. However, the chassis cannot move solely vertically with respect to the track or wheel assemblies or the axis of the pivot pin. Therefore, the track or wheel assemblies cannot move together vertically and independently of the chassis. This can adversely effect the ride or comfort of the vehicle, and can sometimes prevent a track assembly from maintaining contact with the terrain. To solve this problem, some commercially available vehicles include a front support beam which is mounted to rubber blocks on either side of the frame. However, it is desired to have a walking beam suspension which permits independent oscillating and vertical translating motion of the walking beam.
A walking beam suspension is shown in U.S. Pat. No. 5,228,718 but this suspension is designed for trucks, and includes a pair of longitudinally oriented suspension assemblies and requires linear stabilizers to stabilize the assembly in a direction parallel to the pivot axis of the walking beam. Also, with this design, the air bags compress in approximately a 1-to-1 ratio to vertical movement of the pivot axis of the walking beam.